Currently, there are two main types of interference cancellation receivers. Namely, linear minimal mean square error (LMMSE) based interference cancellation receivers and non-linear interference cancellation (NLJC) receivers. LMMSE based interference cancellation receivers estimate the covariance matrix and find the coefficient which is used to achieve the MMSE by solving the large matrix inversion. The minimal required pre-knowledge to use this algorithm in CDMA based communication systems is the desired signal's scrambling and spread code. The NIX based interference cancellation receivers estimate interference items and subtract such items from the received signal in parallel or successively.
These techniques reconstruct the interference items by estimating each interference's amplitude, timing, channel response, and information bit and then remove them from the received signal, based on the pre-knowledge of the desired signal and interference's scrambling and spread codes. Specifically, in wide-band code division multiple access (CDMA) (WCDMA) downlink, the knowledge of variable spreading factors and spread codes of intra-channel and inter-channel interferences is very limited, and an additional algorithm is needed to detect the presence of the interferences.
A significant drawback of these existing interference cancellation techniques is that they require computational complexity and have high requirement for the accuracy of the estimated interference signal in the NLIC receivers. Hence, for these and other reasons, improvements are needed in the art.